h. ray, university of florida1 miniboone e e

H. Ray , University of Florida 1

MINIBOONE

e

e


The Notorious LSND Result

• E =20-52.8 MeV• L =25-35 meters• 3.8 excess• Different from other

oscillation signals• Higher m2

• Smaller mixing angle• Much smaller

probability (very small signal) ~0.3%

e

Posc =sin22 sin2 1.27 m2 L

E


Testing LSND

• Want same L/E• Different detection

method• Different sources of

systematic errors• Test for oscillations

using neutrinos, anti-neutrinos


MiniBooNE Neutrino Beam

• Mesons decay into the anti-neutrino beam seen by the detector

K- / - - +

- e- + + e

• MiniBooNE L/E = 0.5 km / 0.8 GeV (.625)• LSND L/E = 0.03 km / 0.05 GeV (.6)• Anti-nu analysis uses 3.386E20 protons on target


MiniBooNE Detector

• 12.2 meter diameter sphere• Pure mineral oil• 2 regions

Inner light-tight region, 1280 PMTs (10% coverage) Optically isolated outer veto-region, 240 PMTs


Event Signaturecharged-current quasi-elastic events νe p → e+ n


MiniBooNE Analysis

• MiniBooNE is looking for e oscillations

• MiniBooNE is looking for an excess of e

(appearance)

• MiniBooNE performing a blind analysis Some of the info in all of the data

Charge per PMT as a function of time All of the info in some of the data

~oscillation free sample to be open for analysis Low-E NC elastic events, CCQE, CC+

e candidate events locked away until the analysis 100% complete

Same strategy as neutrino mode


Neutrino Mode Result• Used 2 complementary

analyses• ruled out interpretation

of LSND as νμ→νe oscillations two-nu oscillations standard L/E depend. no CP, CPT violation

• Unexplained excess of events in low-energy region Excess incompat. With

2-nu lsnd-style oscillations

Phys. Rev. Lett. 98, 231801 (2007)


Anti-neutrino Analysis• Similarities with neutrino mode

Using two complementary analysesUsing same algorithmsSame event selection cuts

• Changes made wrt neutrino modeAdded an event selection cut that removes

most of the dirt (out of tank) background at low energy

Added k- production systematic error New NC π0 measurementNew dirt fraction extracted


Analysis Chain

Beam Flux Prediction

Cross Section Model

Optical ModelEvent

ReconstructionParticle

Identification

Simultaneous Fit to anti-

and anti- e events

Start with a Geant 4 flux prediction for the nu spectrum from and K produced at the target

Use track-based event reco

Predict nu interactions using the Nuance event generator

Pass final state particles to Geant 3 to model particle, light propagation in the tank

Fit reco. energy spectrum for oscillations

Use hit topology and timing to identify electron-like or muon-like charged current neutrino interactions

Track Based Analysis


Analysis Chain

Beam Flux Prediction

Cross Section Model

Optical ModelEvent

ReconstructionParticle

Identification

Simultaneous Fit to anti-

and anti- e events

Start with a Geant 4 flux prediction for the nu spectrum from and K produced at the target

Use point-source event reco

Predict nu interactions using the Nuance event generator

Pass final state particles to Geant 3 to model particle, light propagation in the tank

Fit reco. energy spectrum for oscillations

Use boosted decision tree to identify electron-like or muon-like charged current neutrino interactions

Boosted Decision tree


Expected Backgrounds

Boosting Analysis Track Based Analysis

500 MeV < Reconstructed Neutrino Energy < 1.25 GeV

Intrinsic e backgrounds mis-id backgrounds

3.386e20 POT


Expected Sensitivity

As in neutrino mode, TBA is the more sensitive (default) analysis.

BDT is the cross-check analysis


Expected Background EventsBackground composition for TBA analysis (3.386e20 POT)

LSND best-fit (Δm2, sin22θ)=(1.2,0.003)

[note: statistical-only errors shown]e from ±, ± 8.44 17.14

e from k±,0 8.20 24.88

Other e 1.11 1.21

CCQE 2.86 1.24

NC 0 24.60

7.17

Delta Rad 6.58 2.02

Dirt 4.69 1.92

Other 3.82 2.20

Total Bgd 60.29

57.78

LSND Best Fit 4.33 12.63

Intr

insi

c e

m

is-i

d

200-475 MeV

475-1250 MeV


Systematic Uncertainties

Source

EνQE range (MeV) 200-475 475-

1100200-475 475-

1100

Flux from π+/μ+ decay

0.4 0.7 1.8 2.2

Flux from π-/μ- decay

3.3 2.2 0.1 0.2

Flux from K+ decay 2.3 4.9 1.4 5.7

Flux from K- decay 0.5 1.1 - -

Flux from K0 decay 1.5 5.7 0.5 1.5Target and beam models 1.9 3.0 1.3 2.5

ν-cross section 6.4 12.9 5.9 11.9NC π0 yield 1.7 1.6 1.4 1.9

Hadronic interactions 0.5 0.6 0.8 0.3

External interactions (dirt) 2.4 1.2 0.8 0.4

Optical model 9.8 2.8 8.9 2.3

Electronics & DAQ model 9.7 3.0 5.0 1.7

Total (unconstrained) 16.3 16.2 12.3 14.2

From fits to world’s data (HARP, Kaon production)

Track Based AnalysisAntinu Mode Nu Mode



Source


1100200-475 475-

1100

Flux from π+/μ+ decay 0.4 0.7 1.8 2.2

Flux from π-/μ- decay 3.3 2.2 0.1 0.2



Flux from K0 decay 1.5 5.7 0.5 1.5

Target and beam models 1.9 3.0 1.3 2.5

ν-cross section 6.4 12.9 5.9 11.9

NC π0 yield 1.7 1.6 1.4 1.9Hadronic interactions 0.5 0.6 0.8 0.3

External interactions (dirt)

2.4 1.2 0.8 0.4





Internal MB measurements

Antinu Mode Nu Mode



Source


1100200-475 475-

1100






Target and beam models

1.9 3.0 1.3 2.5

ν-cross section 6.4 12.9 5.9 11.9

NC π0 yield 1.7 1.6 1.4 1.9




Electronics & DAQ model

9.7 3.0 5.0 1.7


Track Based AnalysisAntinu Mode Nu Mode

Determined by special runs of the beam MC. All beam uncertainties not coming from meson production by 8 GeV protons are varied one at a time. variations are treated as 1σ excursions, prop into a final error matrix.

Uncert. in a number of hadronic processes, mainly photonuclear interaction final state

uncertainties in light creation, propagation, and detection in the Tank. Use set of 130 MC “multisims” that have been run where all these parameters are varied according to their input uncertainties.



Source


1100200-475 475-

1100






Target and beam models 1.9 3.0 1.3 2.5

ν-cross section 6.4 12.9 5.9 11.9

NC π0 yield 1.7 1.6 1.4 1.9







Fit to the anti-νμ CCQE and anti-νe candidate spectra simultaneously. takes advantage of strong correlations between anti-νe signal, background, and the anti-νμ CCQE sample, reduces systematic uncertainties and constrains intrinsic anti-νe from muon decay

Antinu Mode Nu Mode

Antineutrino appearance search is statistics limited!


Counting Expt :475 MeV < E

QE< 1.250 GeV61 observed evts57.8 ± 10.0 expected eventsExcess over background : 0.3

Counting Expt :200 MeV < E

QE< 475 MeV61 observed evts61.5 ± 11.7 expected eventsExcess over background : -0.04

Observed Event Distribution


Excess Distribution

(Δm2, sin22θ) = (4.4 eV2, 0.004)

χ2best-fit(dof) = 18.18 (17)

χ2-probability = 37.8%


EνQE range (MeV) anti-ν mode ν mode

(3.386e20 POT) (6.486e20 POT)

200-300

300-475

200-475

475-1250

Excess

Deficit

Data 24 232MC ± sys+stat (constr.) 27.2 ± 7.4 186.8 ± 26.0Excess (σ) -3.2 ± 7.4 (-0.4σ) 45.2 ± 26.0 (1.7σ)

Data 37 312MC ± sys+stat (constr.) 34.3 ± 7.3 228.3 ± 24.5Excess (σ) 2.7 ± 7.3 (0.4σ) 83.7 ± 24.5 (3.4σ)


Data 61 408MC ± sys+stat (constr.) 57.8 ± 10.0 385.9 ± 35.7Excess (σ) 3.2 ± 10.0 (0.3σ) 22.1 ± 35.7 (0.6σ)

arXiv:0812.2243

Event Summary


Same ν and ν NC cross-section (HHH axial anomaly), POT scaled, Low-E Kaon scaled: strongly disfavored as an explanation of the MiniBooNE

low energy excess!

most preferred modeL: low-energy excess comes from neutrinos in the beam (no contribution from anti-neutrinos)

Currently in process of more careful consideration of correlation of systematics in neutrino and antineutrino mode… results coming

soon!

Stat Only Correlated Syst Uncorrelated Syst

Same ν,ν NC 0.1% 0.1% 6.7%NC π0 scaled 3.6% 6.4% 21.5%POT scaled 0.0% 0.0% 1.8%Bkgd scaled 2.7% 4.7% 19.2%CC scaled 2.9% 5.2% 19.9%Low-E Kaons 0.1% 0.1% 5.9%ν scaled 38.4% 51.4% 58.0%

Maximum χ2 probability from fits to ν and ν excesses in 200-475 MeV range

Preliminary

(upper and lower bounds)

_

_

Implications for Low-E Excess


Final Limits

• No strong evidence for oscillations in anti-nu mode Analysis limited by stat

• No evidence of excess at low energy in anti-nu mode Combine nu, anti-nu for

low-E analysis

• Data collection continuing through June, 09

• NuMI analysis in 2009!

3.386e20 POT

Backup Slides


The Notorious LSND

• 800 MeV proton beam + H20 target, Copper beam stop

• 167 ton tank, liquid scintillator, 25% PMT coverage

• E =20-52.8 MeV

• L =25-35 meters

• e + p e+ + n n + p d + (2.2 MeV)

e


Neutrino Event Composition

Boosting Analysis

Other12%

NCpi018%

Rad. Delta4%

K+26%

Ko6%

Pi+1%

Mu+33%

Likelihood Analysis

intrinsic e

mis-id


Flux Prediction

• Much larger wrong sign component in anti-neutrino analysis

nu mode Anti-nu mode

Intrinsic background to oscillation

analysis

Intrinsic background to oscillation

analysis

Wrong sign

contamination Wrong sign

contamination


Systematic Errors• Use Multisims to calculate

systematic errors• In each MC event vary all

parameters at once, according to a full covariance matrix Ex : Feynman scaling of K+

varies 8 params simultaneously

• Vary full set of parameters many times per event

• OM = 70 multisims. All other errors = 1000

• Use this information to form an error matrix

Central Value MC

#evts in 1 E bin

# m

ult

isim

s K+ error


Systematic ErrorsError Track vs

Boosting (%)

Checked or Constrained by

data

DAQ 7.5 / 10.8

Target/Horn 2.8 / 1.3

+ Flux 6.2 / 4.3

K+ Flux 3.3 / 1.0

K0 Flux 1.5 / 0.4

Dirt 0.8 / 3.4

NC 0 yield 1.8 / 1.5

Neutrino Xsec 12.3 / 10.5

OM 6.1 / 10.5


Expected Event Composition

W+

p

n

μ+ can……capture on C…decay too quickly…have too low energy

Nevents 200-475 MeV 475-1250 MeV

intrinsic νe 17.7443.23from π±/μ± 8.44 17.14from K±, K0 8.20 24.88other νe 1.11 1.21

mis-id νμ 42.54 14.55CCQE 2.86 1.24NC π0 24.60 7.17Δ radiative 6.58 2.02Dirt 4.69 1.92other νμ 3.82 2.20

Total bkgd 60.29 57.78

LSND best fit 4.33 12.63



Z

A






Coherent π0 production

A

γ

γ



Z

p






Resonant π0 production

p

γ

γ



Z

p






…and some times… Δ radiative decay

p



shower

dirt






MiniBooNE detector


How consistent are excesses in neutrino and antineutrino mode under different underlying hypotheses as the source of the low energy excess in neutrino mode?


200-475 MeV νν_

Scales with POT Same NC cross section for neutrinos and antineutrinos Scales as π0 background Scales with neutrinos (not antineutrinos) Scales with background Scales as the rate of Charged-Current interactions Scales with Kaon rate at low energy



200-475 MeV

• Performed 2-bin χ2 test for each assumption• Calculated χ2 probability assuming 1 dof

The underlying signal for each hypothesis was allowed to vary (thus accounting for the possibility that the observed signal in neutrino mode was a fluctuation up, and the observed signal in antineutrino mode was a fluctuation down), and an absolute χ2 minimum was found.

• Three extreme fit scenarios were considered: Statistical-only uncertainties Statistical + fully-correlated systematics Statistical + fully-uncorrelated systematics

νν_


Eg.: scales with POT (e.g. “paraphotons”,…)

Antineutrino POT: 3.386e20 Antineutrino POTNeutrino POT: 6.486e20 Neutrino POT

One would expect a ν excess of ~(128.8 events)*0.52 = ~67 events


200-475 MeV

Obviously this should be highly disfavored by the data, but one could imagine a scenario where the neutrino mode observed excess is a fluctuation up from true underlying signal and the antineutrino mode excess is a fluctuation down, yielding a lower χ2…

= 0.52

νν_


Eg.: Same NC cross section for neutrinos and antineutrinos (e.g., HHH axial anomaly)

Expected rates obtained by integrating flux across all energies for neutrino mode, and antineutrino mode


200-475 MeV νν_

[Harvey, Hill, and Hill, hep-ph0708.1281]


Eg.: Scales as π0 background (same NC ν and ν cross-section ratio)

Expected rates obtained by integrating flux across all energies for neutrino mode, and antineutrino mode

Mis-estimation of π0 background? Or other Neutral-Current process?

For π0 background to fully account for MB ν mode excess, it would have to be mis-estimated by a factor of two……but we have measured MB π0 event rate to a few percent!


200-475 MeV νν_

[Phys. Lett. B664, 41 (2008)]

_


Eg.: Scales with neutrinos (in both running modes)

In neutrino mode, 94% of flux consists of neutrinosIn antineutrino mode, 82% of flux consists of antineutrinos, 18% of flux consists of neutrinos

Predictions are allowed to scale according to neutrino content of the beam


200-475 MeV νν_


χ2null(dof)1

χ2best-fit(dof)1 χ2

LSND best-

fit(dof)χ2-prob χ2-prob χ2-prob

20.18(19) 18.18(17) 20.14(19)38.4% 37.8% 38.6%

17.88(16) 15.91(14) 17.63(16)33.1% 31.9% 34.6%

EνQE fit

> 200 MeV

> 475 MeV

EνQE > 200 MeV and Eν

QE > 475 MeV fits are consistent with each other.No strong evidence for oscillations in antineutrino mode.

(3.386e20 POT)

(1Covariance matrix approximated to be the same everywhere by its value at best fit point)


2D global fit

h. ray, university of florida1 miniboone e e

Documents

anti e eventsstart

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nu spectrum

antinu analysis

antineutrino beam

e oscillations miniboone

neutrino modeusing